Particulate matter (PM) is included in a gas exhausted from an internal combustion engine such as a diesel engine or various combustion devices. When the PM is released into the atmosphere, a particulate filter for collecting the PM is mounted in the exhaust system of the exhaust gas for environmental reasons.
The particulate filters may be divided into a flow-through type particulate filter and a wall flow type particulate filter depending on a flow of the fluid, or exhaust gas. According to the flow-through type particulate filter, the fluid inflowing to one channel does not flow to other channels, but flows in only one channel. Accordingly, the increasing of the back pressure is minimized, however a means to collect the particulate matter included in the fluid is required and a filter performance may be deteriorated. In the wall flow type particulate filter, the fluid inflowing in one channel moves to neighboring other channel and is then exhausted from the particulate filter through the other channel. That is, the fluid inflowing to the inflow channel moves to an outflow channel through a porous wall, and is exhausted from the particulate filter through the outflow channel.
When the fluid passes through the porous wall, the particulate matter included in the fluid does not pass the porous wall, but is collected. In the wall flow type particulate filter, the back pressure may increase, however the wall flow type particulate filter is effective in filtering the particulate matter. Accordingly, the wall flow type particulate filter is often used. In the vehicle, at least one catalytic converter is mounted along with the particulate filter. The catalytic converter is configured to purify a carbon monoxide (CO), a hydrocarbon (HC) and a nitrogen oxide (NOx) included in the exhaust gas. The catalytic converter may be mounted to be physically separated from the particulate filter, and may be merged to the particulate filter by coating the catalyst to the particulate filter.
The particulate filter coated with the catalyzed is referred to a catalyzed particulate filter (CPF). In the CPF, the catalyst is coated at the porous wall dividing the inflow channel and the outflow channel, and the fluid passes through the porous wall and is contacted with the coated catalyst. A pressure difference may exist between the inflow channel and the outflow channel divided by the porous wall, and thereby the fluid quickly passes the porous wall. Accordingly, the contact time of the catalyst and the fluid is short such that the catalyst reaction is not sufficiently generated. Also, if the catalyst coated to the porous wall is thick, the catalyst may block, or partially block, the micro pore formed at the wall such that the flow of the fluid from the inflow channel to the outflow channel may be reduced. Accordingly, a back pressure increases.
To minimize the increasing of the back pressure, the catalyst is thinly coated in the CPF. Accordingly, the amount of the catalyst coated in the CPF is such that the catalyst reaction may be not sufficiently generated. To solve these problem, by increasing a number of the inflow channels and the outflow channels (hereinafter, commonly referred to as cell), a surface of the wall in which the catalyst is coated may increase. However, if the density of the cell increases in the limited space, the thickness of the wall may be decreased. The reduction of the thickness of the wall may cause a deterioration of the filter performance. Accordingly, the density of the cell may not increase by more than a limit density.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.